Differential distribution of basement membrane type IV collagen α1(IV), α2(IV), α5(IV) and α6(IV) chains in colorectal epithelial tumors

In this study, we examined the relationship between the histopathological grade and immunohistochemical localization of six genetically distinct type IV collagen α chains, the major component of basement membrane (BM), in normal and neoplastic colorectal tissues. In the normal colorectal mucosa, α1/α2(IV) and α5/α6(IV) chains were stained in all epithelial BM. However, α3/α4(IV) chains were restrictively immunostained in the BM of the apical surface epithelium. Similar immunostaining profiles for α1/α2(IV) and α5/α6(IV) chains were observed in tubular adenomas with mild/moderate atypia. However, in intramucosal carcinomas, both α1/α2(IV) chains were linearly stained in the BM of cancer cell nests, while the assembly of α5/α6(IV) chains into the BM was inhibited in a discontinuous or negatively stained pattern. The normal colorectal mucosa forms a second network of BM composed of α5/α6(IV), partly α3/α4(IV) chains, in addition to the classic network of α1/α2(IV) chains. The differential immunohistochemical localization of the type IV collagen α5/α6 chains could be one diagnostic marker for the invasiveness of colorectal cancer.